The human body is far too complicated to be easily replaced by artificial parts, and the upper airway is no exception. The upper airway performs a multitude of functions, the simplest being that of a conduit from the atmosphere to the lungs. Other important functions of the upper airway include humidification and filtration of air, mounting of an immune response to outside infectious agents, removal of debris by deglutition (swallowing) and expectoration (spitting), and speech.
Tracheal tubes are artificial conduits which are commonly inserted into an individual's trachea to enable them to breathe, or to deliver anesthetic gases to an unconscious patient. Tracheal tubes are often required to artificially ventilate an individual in critical clinical situations. While helpful to secure airways and save lives, tracheal tubes can interfere with the other important upper airway functions of the trachea. If they are needed for an extended period of time, tracheal tubes can also be destructive to the surrounding tissues and organs.
Tracheal tubes include both tracheostomy tubes and endotracheal tubes. A tracheostomy tube is inserted through a surgically produced opening in the anterior neck (i.e. through a tracheotomy). An endotracheal tube is inserted into the trachea through the mouth or nose, and is usually formed without a sharp bend, but otherwise is substantially similar to the tracheostomy tube.
Currently tracheostomy tubes come as either a pre-curved tube or a malleable tube that curves once inserted. The disadvantage of a pre-curved tube is that the curve may not suit an individual's particular anatomy, and therefore the tip of the tube may impinge upon the anterior or posterior wall of the trachea. In some individuals, flexion and extension of the neck may also contribute to the tip of the tube impinging on the tracheal wall. The disadvantage of a flexible tube is that the default shape of the tube is straight, and although it will conform to the curve of the tracheostomy tract, it will have a tendency to impinge the posterior wall of the trachea.
One fundamental dilemma common to all tracheal tube designs is that they must have at least some rigidity in order not to kink or collapse, otherwise they are not effective conduits for air, yet they must be gentle on the airway structures. Unfortunately, the rigidity of the tubes invariably causes some force to be applied to the mucosa of the trachea. Tracheal tubes routinely exert pressures far in excess of the mucosal perfusion pressure at the points of contact with the mucosa, such that blood flow, oxygen delivery and waste removal at the points of contact are diminished.
Even despite devoted clinical care, tracheal tubes routinely result in ischemic areas of the tracheal mucosa. Indeed, the complications associated with prolonged intubation can be particularly severe. Persistent irritation of the cartilaginous support of the trachea causes destruction of structures. Later, scarring and stricture formation will result within the trachea once the irritation is removed. Ischemia routinely results in pressure necrosis, ulceration, granulation formation and scarring of the tracheal mucosa. Long term use of a tracheostomy tube often leads to suprastomal granulation tissue formation, suprastomal collapse, and tracheal wall erosion due to the tip of the tube impinging on the interior tracheal wall. As a result, chronic laryngotracheal stenosis can result (which may require a permanent tracheostomy), as well as tracheomalacia, formation of fistulae between the trachea and the esophagus, and erosion of the innominate artery next to the trachea.
In individuals with tracheomalacia, a mobile trachealis (a muscle along the back wall of the trachea) may bulge anteriorly and partly occlude the open distal end of a tracheal tube. This problem arises because the open distal ends of currently used tracheostomy tubes have tips that are cut flush at a 90° angle to the shaft. A secondary problem that arises at the distal end of the tube is that deep suctioning of secretions through the tube may cause damage (granulation or stenosis) to the trachea and bronchi. This occurs because the suction catheter used to perform this maneuver is typically unknowingly extended past the tip of the tube and makes contact with the tracheal and bronchial surfaces, thereby causing the damage.
There exists tracheostomy tubes in the prior art which are designed to minimize damage to the tracheal mucosa. For example, U.S. Pat. No. 4,340,046 to Cox provides a flexible, corrugated, unitary tracheostomy tube. The flexibility so provided is intended to allow the tube to follow lateral movements of the head and neck without significant resistance to those movements, and to adapt to the contour of the neck and trachea. This serves to prevent the end of the tube from scraping the tracheal wall as severely as a more rigid tracheal tube does. U.S. Pat. No. 4,987,895 to Heimlich discloses a tracheostomy tube with a corrugated, flexible and collapsible middle section which allows the tube to elongate and contract during swallowing and respiration in an attempt to reduce rubbing of the tube against the tracheal wall. The tip of the Heimlich tube is intended to remain in a constant position relative to the tracheal mucosa it lies against. In theory this will limit the “rubbing” of the mucosa by either the tip or the cuff of the tracheostomy tube.
While prior art tracheostomy tubes may be useful for their intended purpose, there still exists a need for a tracheostomy tube for patients suffering from tracheomalacia which causes less ischemic areas of the tracheal mucosa, resulting in a decreased tendency to produce rubbing, pressure necrosis, ulceration and scarring of the tracheal mucosa.